Particulate filters may be utilized in vehicle exhaust systems to trap carbonaceous soot that may be exhausted from an internal combustion engine. Once particulate matter is stored in the particulate filter, it may be oxidized and released from the particulate filter as carbon dioxide. The oxidation proceed may reduce vehicle fuel efficiency. Therefore, it may be desirable to only oxidize or regenerate the particulate filter when a desired amount of particulate matter has accumulated within the particulate filter. One way to estimate an amount of particulate matter stored within a particulate filter is based on a pressure change across the particulate filter. However, pressure sensors add cost to an exhaust system and may become plugged with soot. Another way to estimate soot trapped in a particulate filer is to estimate soot output of an engine via a model and use the model output as an estimate of soot stored in the particulate filter. Nevertheless, modeling errors and varying operating conditions may result in particulate matter estimates that invoke filter regeneration more or less frequent than is desired. Thus, it may be desirable to estimate an amount of soot stored in a particulate filter in a way that may be more cost effective than using pressure sensors and more accurate than an engine particulate matter model.
The inventors herein have recognized the above-mentioned issues and have developed a method for regenerating a particulate filter, comprising: estimating an amount of water stored within the particulate filter; and regenerating the particulate filter in response to the amount of water stored.
By regenerating a particulate filter in response to an amount of water stored in the particulate filter, it may be possible to provide the technical result of regenerating a particulate filter without the added cost of pressure sensors and at conditions when particulate filter regeneration is desired. In one example, output of existing upstream and downstream oxygen sensors is a basis for determining an amount of water stored within a particulate filter during an engine cold start. The amount of water stored within the particulate filter may be correlated to an amount of soot held within the particulate filter because the soot tends to increase the amount of water a particulate filter may store. In this way, an estimate of water stored in a particulate filter may be a basis for determining an amount of soot stored in the particulate filter and initiating particulate filter regeneration.
The present description may provide several advantages. Specifically, the approach may provide timely particulate filter regeneration without the added expense of exhaust pressure sensors. Further, the approach may initiate particulate filter regeneration using existing sensors so that additional sensor diagnostics are not required. Further still, the approach may provide a more accurate estimate of an amount of soot stored within a particulate filter than other estimation methods.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.